update. Went to a mechanic near my place, a very experienced fellow. He knew immediately my ignition timing was off. He proceed to remove the distributor, cleaned it up, and changed the oil seal and o ring. He also re adjusted the tappets. He then re set the ignition timing, to where he said it was supposed to be. Then he backed off on the carb idle.
the diagnosis was , I retarded the distributor because I was hearing pinging sounds thinking it was detonation, then compensated by increasing the idle speed screw to maintain the correct idle speed. he said I was only masking the real problem, which was in his opinion, con rod bearings. I told him my oil pressure is fine, but he said could be only one or two bearings giving the problem. He said changing the crankshaft and getting the correct bearings would cost a lot of money, and he suggested a used half cut engine swap. The money he asked for wasn't astronomically high, about 500 USD for the engine swap , that includes labor cost. So I definitely am interested to try this out. Besides, the UOA's I have been doing seem to support what he said, I find about 25ppm of lead in a OCI of 15000km.
I will stop doing UOAs on this engine and if I do swap engine I will do a UOA to check and compare.
perhaps the break in wasn't done correctly 11 years back, or the guy who did the overhaul did not grind the crankshaft properly to spec with the correct bearings.
The engine runs fine except for that metallic rattling on low rpm acceleration.